1. Field of the Invention
The present invention relates to an information recording medium such as an optical disc medium having a defect information area, a defect management method for managing defect management information written on a defect information area, an information reading/writing device and an information reading device in which an information recording medium having a defect information area is used.
2. Related Art
A kind of optical disc medium has a user area for storing user data and a spare area which is reserved, and is so configured as to perform alternation processing for replacing a defect area caused in the user area with a sound area in the spare area. An area for recording defect management information relating to the alternation processing is called DMA (defect management area) which requires high reliability.
Each time the alternation processing is performed, replacement information is added, so defect management information which should be written on the DMA must be updated, whereby overwrite frequency of the DMA is relatively high. For example, a DVD-RAM is so adapted that overwrite of a DMA is possible for more than one-hundred thousands times, and DMAs storing the same contents are provided at four locations so as to secure high reliability.
On the other hand, in an information recording medium with low durability against overwrite, such countermeasures as disclosed in the publication of Japanese Patent Application Laid-open No. 2004-39076 (Patent Document 1) and the publication of Japanese Patent Application Laid-open No. 2004-288285 (Patent Document 2) are proposed.
Patent Document 1 discloses a method of securing reliability of defect management information in which a plurality of DMAs, on which defect management information of the same content is written, forms a set of DMAs (DMA set), and a defect information area is prepared in which a plurality of DMA sets are provided, and when a DMA set in use is deteriorated to be defective due to overwrite, another DMA set within the defect information area is used so as to secure reliability.
Patent Document 2 discloses a system in which, besides a defect information area consisting of a plurality of DMA sets capable of recording defect management information, there is provided a selection information area for recording selection information indicating a DMA set on which the latest defect management information within the defect information area is written, and based on the selection information of the DMA set stored on the selection information area, the DMA set on which the latest defect management information is written is specified in a short time. The selection information is called a DMA manager. The DMA manager is written on a DMA manager area. Similar to the case of writing the defect management information, a plurality of DMA manager areas on which selection information of the same content for selecting a DMA set is recorded forms a set of DMA managers (DMA manager set), whereby it is possible to enhance reliability of the selection information for selecting a DMA set. Further, by constituting the selection information area so as to include a plurality of DMA manager sets, it is also possible to cope with deterioration of a DMA manager set due to overwrite.
However, in a case of adopting a configuration in which a DMA manager set consists of a plurality of DMA manager areas, there has been a following problem.
That is, when updating selection information of the DMA set, there may be a case where the selection information cannot be written on a part of the DMA manager areas due to such reasons as a halt of an information reading/writing device due to sudden power discontinuity or reset, and disc recording defect due to stains on the disc surface of the optical disc medium. In such a case, an abnormal state is caused, that is, selection information written on a DMA manager area does not match with selection information written on another DMA manager area in the information recording medium while those DMA manager areas belong to the same DMA manager set. In such a case, reliable selection information cannot be obtained. When the selection information cannot be obtained, although it is possible to select the latest DMA set by directly searching DMA sets, it takes long time to obtain the result if the number of DMA sets to be searched is large.